1. Field of the Invention
The present invention relates to a luminance signal/chrominance signal separation filter which separates luminance signal (hereinafter to be called Y signal or simply Y) and chrominance signal (hereinafter to be called C signal or simply C) independently from composite video signal (hereinafter to be called V signal) which is obtained by frequency-multiplexing C signal in high frequency band of Y signal, particularly to a Y/C separation filter which is adaptive to motion image.
2. Related Art of the Invention
A motion-adaptive Y/C separation filter judges partially whether an image is static or moving and carries out Y/C separation suitable for pixel signal of the respective portions. The present filtering of NTSC signal uses a V signal which is a composite signal obtained by frequency-multiplexing C signal in high frequency band of Y signal. Therefore, a receiver is necessary to undergo Y/C separation, and incomplete separation causes picture quality degradation such as cross color or cross luminance. Accordingly, various kinds of signal processing circuits for improving picture quality such as motion-adaptive Y/C separation ion utilizing a delay circuit having delay time being equal to or higher than vertical scanning frequency (hereinafter, to be called simply a delay circuit) have been proposed. This depends upon the fact that a memory of vast capacity has been developed and utilized for image processing.
FIG. 1 is a block circuit diagram showing an example of a conventional motion-adaptive Y/C separation filter.
In FIG. 1, to an input terminal 1, V signal 201 of NTSC method is inputted to be given to respective input terminals of a filter 4 for extracting an intrafield Y signal, a filter 5 for an extracting interframe Y signal, a color demodulation circuit 6 and a motion detecting circuit 11 for Y signal.
Y signal 202 by intrafield Y/C separation which has undergone Y/C separation by the filter 4 for extracting intrafield Y signal is inputted into a first input terminal of a mixing circuit 14 for Y signal, and Y signal 203 by interframe Y/C separation which has undergone Y/C separation by the filter 5 for extracting interframe Y signal is inputted to a second input terminal of the mixing circuit 14 for Y signal.
In addition, V signal is color-demodulated into two kinds of color difference signals, that is, R-Y signal and B-Y signal. The two kinds of color difference signals are time-divisionally multiplexed by the frequency of a time divisional multiplexer 7. The frequency band of the output signal of the time divisional multiplexer 7 is band-limited by a low-pass filter 8 (hereinafter, to be called LPF) which allows a band lower than 1.5 MHz to be passed. A color difference signal 204 which is band-limited is inputted to respective input terminals of a filter 9 for extracting C intrafield signal, a filter 10 for extracting interframe C signal, and a motion detecting circuit 12 for C signal.
C signal 205 by intrafield Y/C separation which has undergone Y/C separation by the filter 9 for extracting intrafield C signal is inputted to a first input terminal of a C signal mixing circuit 15. In addition, C signal 206 by Y/C separation in a frame which has undergone Y/C separation by the filter 10 for extracting interframe C signal is inputted to a second input terminal of the mixing circuit 15 For C signal.
On the other hand, a signal 207 showing the amount of motion of Y signal detected by the motion detecting circuit 11 for Y signal is inputted to one input terminal of a synthesizer 13, and a signal 208 showing the amount of motion of C signal detected by the motion detecting circuit 12 for C signal is inputted to the other input terminal of the synthesizer 13.
A motion detecting signal 209 which has been synthesized by the synthesizer 13 is inputted to a third input terminal of the mixing circuit 14 for a Y signal and to a third input terminal of the mixing circuit 15 for a C signal respectively, and a motion detecting unit 80 is composed of the motion detecting circuit 11 for Y signal, motion detecting circuit 12 for C signal and synthesizer 13. A Y signal 210 by motion adaptive Y/C separation which is an output of the mixing circuit 14 for Y signal is outputted From an output terminal 2, and a C signal 211 by motion adaptive Y/C separation which is an output of the mixing circuit 15 for C signal is outputted from an outpost terminal 3.
Next, explanation will be given of the operation. In separating a V signal 201, the motion detecting unit 80 judges whether V signal 201 is a signal showing a static image or a moving image by synthesizing respective outputs of the motion detecting circuit 11 for Y signal and the motion detecting circuit 12 for C signal by the synthesizer 13.
The motion detecting circuit 11 for Y signal, as shown in FIG. 2 for example, subtracts at a subtracter 83 a signal which has been obtained by making the V signal 201 inputted from an input terminal 21 to be delayed by one frame at one-frame delay circuit 82 from the directly inputted V signal 201 to calculate one-frame difference, and passes it through a LPF 84 which allows band lower than 2.1 MHz to be passed, then calculates the absolute value thereof at an absolute value circuit 85 and changes it into a signal 207 showing the amount of motion of low frequency component of Y signal at a non-linear transform circuit 86 to output it to an output terminal 81.
The motion detecting circuit 12 for C signal, as shown in FIG. 3 for example, subtracts at a subtracter 89 a signal which has been obtained by making the band-limited color difference signal 204 inputted from the input terminal 23 to be delayed by two frames at a two-frame delay circuit 88 from the directly inputted color difference signal 204 to calculate a two-frame difference, and calculates the absolute value at an absolute value circuit 90. Then the absolute value is changed at a non-linear transform circuit 91 to the signal 208 showing the amount of motion of C signal to be outputted from an output terminal 87.
The synthesizer 13 is so constructed, for example, as to select the larger value between the amount of motion of Y signal 207 and that of C signal 208 and output it. The result of discrimination is expressed by motion coefficient K (0.ltoreq.K.ltoreq.1). For example, in the case where an image is discriminated as a complete static image, K=0, and in the case where an image is discriminated as a complete motion image, K=1. It is given as a control signal 209.
Generally, in the case where an image is a static one. Y/C separation is carried out by the filter 5 for extracting interframe Y signal and the filter 10 for extracting interframe C signal utilizing interframe correlation to separate Y signal from C signal.
The filter 5 for extracting interframe Y signal, as shown in FIG. 4 for example, adds at an adder 94 a signal which has been obtained by making the V signal 201 inputted From the input terminal 21 to be delayed by one-frame at a one-frame delay circuit 93 to the directly inputted V signal 201 to calculate a one-frame sum, then extract YF signal 203 to output it to an output terminal 92.
The filter 10 for extracting an interframe C signal, as shown in FIG. 5 for example, adds at an adder 100 a signal which has been obtained by making the color difference signal 204 inputted from the input terminal 23 to be delayed by one-frame at a one-frame delay circuit 99 to the directly inputted color difference signal 204 to calculate a one-frame sum, then extract CF signal 206 to output it to an output terminal 98.
In addition, in the case where an image is a moving one, Y/C separation a is carried out to separate Y signal from C signal by the filter 4 for extracting intrafield Y signal and the filter 9 for extracting intrafield C signal utilizing intrafield correlation.
The filter 4 for extracting intrafield Y signal, as shown in FIG. 6 for example, adds at an adder 97 a signal which has been obtained by making the V signal 201 inputted from the input terminal 21 to be delayed by one-line at a one-line delay circuit 96 to the directly inputted V signal 201 to calculate one-line sum, then extracts Yf signal 202 to output it from an output terminal 95.
The filter 9 for extracting intrafield C signal, as shown in FIG. 7 for example, adds at an adder 103 a signal which has been obtained by making the color difference signal 204 inputted from the input terminal 23 to be delayed by one-line at a one-line delay circuit 102 to the directly inputted color difference signal 204 to calculate one-line sum, then extracts the Cf signal 205 to output it from an output terminal 101.
In a motion-adaptive Y/C separation filter, such filters as the filter 4 for extracting intrafield Y signal and filter 5 for extracting interframe Y signal are juxtaposed and outputs Y signal 210 by motion adaptive Y/C separation from an output terminal 2 by making the mixing circuit 14 for Y signal carry out the following operation according to a control signal 209 being a motion coefficient K synthesized by the motion detecting circuit 12 for C signal. EQU Y=kYf+(1-k)YF
Here,
Yf : output 202 of Y signal by intrafield Y/C separation PA1 YF: output 203 of Y signal by interframe Y/C separation. PA1 Cf: output of C signal by intrafield Y/C separation PA1 CF: output 206 of C signal by interframe Y/C separation
In the above filter, the filter 9 For extracting intrafield C signal and the filter 10 for extracting interframe C signal are juxtaposed in the same way, and outputs C signal 211 by motion adaptive Y/C separation from the output terminal 3 by making the mixing circuit 15 for C signal carry out the following operation according to the control signal 209. EQU C=kCf+(1-k)CF
Here,
As the conventional motion-adaptive Y/C separation filter is so constructed as the above, Yf signal by the filter 4 for extracting intrafield Y signal and the YF signal by the filter 5 for extracting interframe Y signal are to be mixed according to of the synthesized amount of motion detected respectively by the motion detecting circuit 11 for Y signal and the motion detecting circuit 12 for C signal. In the same way, Cf signal by the filter 9 for extracting intrafield C signal and CF signal by the filter 10 for extracting interframe C signal are to be mixed according to the synthesized amount of motion.
Accordingly, as there is an excessive change in resolution in the case where an image changes to a motion one from static one, or vice versa because a filter characteristic of static image is totally different from that of motion one, there has been a problem that picture quality degradation in processing motion image is prominent.